Closure for exhaust stack

ABSTRACT

A stack closure for closing the exhaust end of an exhaust stack to prevent the exhaust of gases from the stack and for opening the exhaust end when desired. A pivotable support frame is connected to a base member located at the exhaust end. A cap is connected to the frame by a floating connection for providing random movement between the cap and the frame. The frame pivots to move the cap into and out of closing engagement with the base and the floating connection permits self-alignment of the cap with the base during closing. Resilient stabilizing members act to stabilize the random movement between the cap and the frame. A seal member seals the cap and base, and pressure limiters protect the seal member from excessive pressure exerted thereon when the cap is in sealing engagement with the base.

United States Patent 11 1 Zarfoss et al.

[111 3,745,907 1451 July 17,1973

[ CLOSURE FOR EXHAUST STACK Koppers Company, Inc., Pittsburgh, Pa.

[22] Filed: May 17,197]

[21] Appl. No.: 144,025

{73] Assignee:

Primary Examiner-William F. ODea Assistant Examiner-Peter D. FergusonAttorney-Boyce C. Dent, Oscar B Brumback and Olin E. Williams [57]ABSTRACT A stack closure for closing the exhaust end of an ex hauststack to prevent the exhaust of gases from the stack and for opening theexhaust end when desired. A pivotable support frame is connected to abase member located at the exhaust end. A cap is connected to the frameby a floating connection for providing random movement between the capand the frame. The frame pivots to move the cap into and out of closingengagement with the base and the floating connection permitsself-alignment of the cap with the base during closing. Resilientstabilizing members act to stabilize the random movement between the capand the frame. A seal member seals the cap and base, and pressurelimiters protect the seal member from excessive pressure exerted thereonwhen the cap is in sealing engagement with the base.

1 Claim, 7 Drawing Figures I PAIENTEUJUUWB 3.145.901

' Q sum 1 M4 INVENTORJy JAMES R. ZARFOSS BY EARLE S. SNADER ELDEN A;HALE SR.

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INVENTOR. JAMES R. ZAR FOSS EARLE S. SNADER ELDEN A. ALE SR.

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INVENTOR JAMES R. ZARFOSS By EARLE S. SNADER I ELDEN A.I ALE SR.

CLOSURE FOR EXHAUST STACK BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates generally to ventilation andspecifically a valved cap for chimneys.

2. Description of the Prior Art Recently, attention has been focused onserious air pollution problems particularly occurring in industrializedareas. Industrial wastes such as exhaust gases are normally dischargedinto the atmosphere. As a result, effective means used to rid theatmopshere of pollutants in exhaust gases have become increasinglyimportant.

One such effective means is the electrostatic precipitator. Whenprecipitators are used, the normally open exhaust end of exhaust stacksmust be closed to divert gases into the precipitator from their path oftravel through the stack. An effective way of closing the exhaust end ofa stack is by using a pivotal closure or cap which may be quickly openedto prevent a backup of the gases in certain situations such as when theprecipitator becomes inoperable. It is important that the cap be capableof effectively sealing the stack for preventing the escape of gases intothe atmposhere and because during the operation of the precipitator theclosed stack is, in effect, merely a piece of ductwork in the gascleaning system and as such is at times required to be under a negativeor positive pressure.

Such an exhaust stack closure is shown in Snader US. Pat. No. 3,545,365including a counterweighted frame and a closure cap having the size andshape of the exhaust end of a stack. The frame is pivotally mounted to abase attached to the top of the stack for sealing engagement with theclosure cap. Such caps are capable of doing an effective job only whenthey properly engage the base to form an effective seal therewith. Thecap is rigidly attached to the pivotal frame and occasionally a cap isinstalled which fails to effectively seal the stack due to slightoffsets or vairations in alignment between the cap and base which mayoccur during manufacture or installation. For example, the cap is weldedto the frame and at times the cap becomes canted slightly out ofalignment with the top of the stack. As a result, an effective seal isnot made since the rigidly connected cap is not able to conform inalignment with the base and only a portion of the cap and base may beengaged whereas a diametrically opposed portion thereof may not evenmake contact due to the rigidity of the cap and frame attachment.Resilient material, placed between the cap and base to aid in sealing,is sometimes damaged or even cut by uneven pres sure resulting fromattempting to positively close the misaligned cap.

It can be seen from the foregoing that it would be advantageous toprovide a reliable cap having the ability to accommodate variations inalignment between the cap and base and thereby automatically self-alignitself with the base to form an effective closure therewith. Also, thereis a need for a resilient seal member to seal the cap and base which isnot subject to damage due to uneven pressure resulting from a misalignedcap.

SUMMARY OF THE INVENTION Accordingly, the present invention provides areliable cap capable of accommodating variations in alignment betweenthe cap and base and thereby aligning with the base to fonn an effectiveclosure therewith. This is accomplished by the use of a floatingconnection between the cap and frame for permitting relativemilti-directional or random movement therebetween rather than theconventional rigid connection. Resilient stabilizers aid in stabilizingthe relative multidirectional movement. Also, the stack closure of thepresent invention has improved sealing capabilities due to the use of aresilient seal member provided between the base member and the cap.Preferably, the seal is made from closed cell silicone sponge rubber.The seal member is not subjected to uneven pressure between the base andcap due to the alignment capabilities of the cap and also due topressure limiters for limiting excessive pressure on the seal member andfor maintaining substantially equal pressure between the cap and theseal member.

The above and other novel features of the invention will appear morefully from the following drawings, the detailed description and theclaims. The drawings are not intended as a definition of the inventionbut are for the purpose of illustration only.

DRAWINGS In the drawings wherein like parts are marked alike:

FIG. 1 is a segmented partial side elevation of an exhaust stackincluding a closure with power means for operating the closure;

FIG. 2 is a plan view of the closure of FIG. 1;

FIG. 3 illustrates a segment of the closure in side elevation andfurther illustrates the cap in closing engagement with the base;

FIG. 4 illustrates a segment of the closure of FIG. 3 and furtherillustrates the cap out of closing engagement with the base;

FIG. 5 illustrates the possible relative multidirectional movementbetween the plates of the floating connection;

FIG. 6 illustrates an enlarged segmented view of one of the resilientstabilizing members connected to the frame and the cap; and

FIG. 7 illustrates an enlarged segmented view of one of the pressurelimiters and its effect on the engagement of the cap and the sealmember. l

DESCRIPTION OF THE PREFERRED EMBODIMENT A stack closure generallydesignated 10 is shown adjacent the exhaust end 12 of an exhaust stack14, FIG. 1. Closure 10 includes a base a frame pivotally connected tobase 20; a cap attached to frame 30 by a floating connection generallydesignated and means for pivoting frame 30 so as to move cap 40 intoclosing engagement with base 20. Floating connection 50 permits relativemulti-directional movement of cap 40 with respect to frame 30.Such'relative movement provides a cap 40 which is capable ofaccommodating variations in alignment between cap 40 and base 20 thuspermitting cap 40 to automatically self-align with base 20 to form aneffective closure therewith. Seal member 21, best shown in FIG. 7,.seals the closure of cap 40 and base 20. Again in FIG. 1, pressurelimiters advantageously limit the pressure exerted on seal member 21 bycap 40 and provide substantially equal pressure therebetween around theperiphery of the seal.

Resilient members 70 are preloaded in compression between frame 30 andcap 40 for stabilizing the relative movement therebetween. Pressurelimiters 60 are provided at locations A, B, C and D, best shown in FIG.2, and resilient members 70 are provided at locations E, F, G and H,also shown in FIG. 2. Frame 30 is pivotable by power means located nearthe base of stack 14, as viewed in FIG. 1, comprising a reversibleelectric motor 80 and a pair of screw jacks 81 and 82 operable forsimultaneously moving cables 83 and 84 in opposite directions so as torotate circular track lever arm 85.

Base 20, FIG. 1, comprises band 22 which encircles and is secured to theexhaust end 12 of stack 14 such as by welding. Band 22 includes upperannular flange 23 and lower annular flange 24 spaced from flange 23,better shown in FIG. 3. Flanges 23 and 24 reinforce band 22 and upperflange 23 provides an annular seat 25 upon which seal member 21 ispreferably mounted. If desired, seal member 21 may be secured to cap 40.

FIGS. 3 and 7 illustrate the mating engagement of base 20 and cap 40including seal member 21 mounted within an annular channel formed byinner ring 26 and outer ring 27 located upon annular seat 25. Sealmember 21 preferably comprises a closed cell silicone resilient materialsuch as closed cell silicone sponge rubber. The closed cell siliconematerial of seal member 21 is substantially non-porous and forms apositive seal between cap 40 and base 20. This is important because,during operation of precipitators, the closed stack is exposed tonegative or positive pressures and therefore an effectively sealed stackis desirable.

FIG. 2 shows bearing mounts 28 and 29 secured to base 20, such as bywelding. Bearing mounts 28 and 29 support bearings 101 and 102. A shaft103 is pivotally mounted in bearings 101 and 102. These bearings arelaterally spaced so that pivot shaft 103 extends between them. Ifdesired, the bearings may comprise metal supports with round or squareholes therein corresponding to the diameter of shaft 103.

Frame 30 includes a main support 31 and parallel supports 32substantially shorter in length than support 31, see FIGS. 1 and 2.Supports 32 are axially adjacent support 31 at equally spaced distanceson opposite sides thereof. Support 31 may comprise an I beam or, ifdesired, two channels may be welded together back to back. Supports 32preferably comprise substantially equivalently sized channels.Counterweight 33, preferably an I beam, shown on the right in both FIGS.1 and 2, is attached to support 31 and supports 32 preferably bywelding. At an opposite end, or on the left as shown in FIG. 2, support31 and supports 32 are connected by cross supports 34 which may besimilar in cross section to supports 32.

At a predetermined point between counterweight 33 and cross supports 34,main support 31 and parallel supports 32 are attached to shaft 103. Inthis manner, frame 30 is pivotable about the centroidal axis of shaft103; the shaft being pivotally mounted in bearings 101 and 102. Y

Counterweight 33, on the right of shaft 103, as viewed in FIGS. 1 and 2,acts to counterbalance the weight of cap 40 attached to frame 30 on theleft of shaft 103. The beneficial effect of counterbalancing the weightof cap 40 is that less force is required by the power means to pivotframe 30 for either closing or opening stack 14.

Cap 40, FIG. 3, comprises a circular plate 41 having a dependingperipheral flange 42. Edge 44 of flange 42 engages seal member 21 toform an effective seal therebetween. Plate 41 is generally flat and isstiffened or reinforced by a plurality of intersecting structuralmembers 43, better shown in FIG. 2. Reinforcing members 43 may be anglesor channels or the like, and are attached to plate 41 preferably bywelding, or by bolts if desired, and act to reinforce or stiffen cap 40.Also, reinforcing members 43 are substantially co-planar with plate 41and frame 30 and are extended radially outwardly from the center of cap40 terminating shortly beyond the outer periphery thereof preferably atequally spaced intervals of at least 90 each although, if desired, moremembers may be placed at smaller equally spaced angular intervals.Furthermore, members 43 are important and useful in the successfulfunctioning of the pressure limiters 60 and resilient stabilizingmembers as will be more fully discussed herein.

Floating connection 50, FIG. 5, comprises upper plate 51; intermediateplate 52; lower plate 53; and shoulder bolts 54.

Upper plate 51 is attached to frame 30, preferably by welding, see FIG.4. Also, when viewed in FIG. 2, it can be seen that upper plate 51 islocated substantially adjacent the center of cap 40 and is intersectedby structural members 31 and 34 of frame 30. In this manner, portions ofplate 51, located between the intersecting members 31 and 34 attached-to the plate, are exposed and provide places for bolts 54 which are notobstructed by structural members.

Lower plate 53, FIG. 4 is attached to intersecting reinforcing members43, preferably by welding. It can be seen that lower plate 53 is locatedsubstantially adjacent upper plate 51 and therefore similarly adjacentthe center of cap 40. Portions of plate 53 are located betweenintersecting structural members 43 and are exposed to provide places forbolts 54 which are not obstructed by structural members, such as thatdescribed for upper plate 51.

Intermediate plate 52 is firmly attached to upper plate 51, such as bywelding. If desired, plate 52 could be an integral portion of plate 51protruding therefrom.

Upper and lower plates 51 and 53 respectively, FIG. 5, beingsubstantially aligned with one another, are provided with aligned boltholes 55 preferably located at equally spaced intervals between theattached structural members'31 and 34 of frame 30, and reinforcingstructural members 43 as previously discussed. Shoulder bolts 54,provided in holes 55, include a shoulder portion 54a which overliesholes 55 so as not to permit bolts 54 to pass through holes 55. Threadedshaft portion 54b of bolts 54 extends through aligned holes 55. Washer56 and hex nut 57 is attached to the end of bolt 54 opposite the endhaving shoulder portion 540. Washer 56 overlies holes 55 in a mannersimilar to that described for shoulder portion 540. Hex nut 57 maintainswasher 56 in the desired position on shaft 54b. When bolts 54 areloosely mounted in holes 55 of plates 51 and 53, and washer 56 and hexnut 57 are attached in place, plates 51 and 53 are secured together inspaced apart relationship for limited relative movement axially alongthe length of shaft 54b; that is, movement of plates 51 and 53 islimited by shoulder 54a and washer 56. Furthermore, the amount oflimited relative movement between spaced apart plates 51 and 53 may beincreased or decreased by adjusting hex nut 57 with respect to shoulder54a. Bolts 54 are further loosely mounted since holes 55 aresubstantially larger in diameter than shaft 54 to permit plates 51 and53 to have relative movement laterally and angularly with respect toeach other and with respect to shaft 54b. Therefore, since plate 51 isattached to frame 30 and since plate 53 is attached to cap 40, theresult is that frame 30 and cap 40 have relative multi-directional orrandom movement within the limits of holes 55, shoulder 54a and washer56 thus permitting cap 40 to automatically self-align with base forpositive closing engagement therewith; that is, the floating typeconnection between cap 40 and frame 30 permits the cap to seek its ownlevel or the level of base 20.

The maximum amount that cap 40 can be canted out of alignment with frame30 is illustrated in FIG. 5 wherein it can be seen that plate 53 iscapable of a substantial amount of misalignment with respect to plate51. This maximum condition would probably only occur when frame 30 ispivoted to a substantially vertical position away from base 20. In themaximum misaligned position, plate 53 may contact either edge 51a ofplate 51 or edge 52a of plate 52. When frame 30 is lowered toward base20 and into a substantially horizontal position, the loosely mounted captends to seek its own level due to gravity, and plate 53 which is firmlyattached to cap 40 will shift position with respect to plates 51 and 52.As frame 30 continues to be lowered, approaching the horizontal positionfor alignment with base 20, plate 53 gradually moves out of contact withedge 52a and ultimately rests upon washers 56 prior to cap 40 contactingbase 20, resulting in a space of separation between plates 52 and 53 asshown in FIG. 4.

Conversely, as frame 30 is raised away from base 20 and into asubstantially vertical position, the loosely mounted cap 40 continues toseek its own level and plate 53 rests on washers 56. Eventually,however, as frame 30 approaches the vertical position cap 40 will becomesubstantially misaligned with respect to frame 30 and plate 53 willcorrespondingly shift position with respect to plates 51 and 52.

FIG. 5 also illustrates, through the alternate positions of plate 53with respect to plate. 51, the substantial amount of misalignment whichcan occur between cap 40 and base 20. For example, FIG. 4 illustratescap 40 out of contact with base 20 as would be the case just prior toclosing engagement as cap 40 is being lowered, or just after cap 40 hasbegun to be raised for opening. Considering, however, the possibilitythat base 20 can be substantially misaligned with respect to pivotalframe 30 when frame 30 is lowered into the horizontal position, thecombination of the separation of plates 52 and 53 due to gravity and thesubstantial multidirectional misalignment which can be accommodated byfloating connection 50 enables cap 40 to compensate for an appreciableamount of misalignment between frame 30 and base 20. It can be seen thatcap 40 is operable for mating alignment with base 20 due to theirrelative multi-directional movement.

When cap 40 has engaged base 20 the cap and base are substantiallyaligned and are in continuous contact along edge 44 of flange 42, FIGS.3 and 7. When such contact is made, frame 30 continues to be lowereduntil plate 52 contacts plate 53. Frame 30 exerts a downward force whichis transferred to cap 40 when plate 52 contacts plate 53. Such downwardforce maintains cap 40 in closing engagement with base 20. Shouldmisalignment occur between base 20 and frame 30, a correspondingmisalignment will occur between plates 52 and 53 so that the downwardforce will be transferred from the frame to the cap when edge 52acontacts plate 53, as best illustrated in FIG. 5.

Of course, if desired, plate 52 could be firmly attached to plate 53instead of to plate 51, or plate 52 could have a slightly roundedconfiguration similar to a segment of a sphere, the main purpose beingto provide a localized point of contact between plates 51 and 53.

Pressure limiters 60, located at A, B, C and D of FIG. 2, advantageouslylimit pressure exerted on seal member 21 by cap 40. FIG. 3 illustratescap 40 in closing engagement with base 20 including edge 44 in sealingcontact with seal member 21. If the downward force exerted on cap 40 byframe 30 were not limited, edge 44 could continue to be forced downwardto contact annular seat 25 of base 20. As a result, seal member 21 mightbe cut or severely damaged by edge 44. Pressure limiters 60 are securedto members 43 of cap 40 and therefore movement of the secured limitersdepends on the multi-directional movement permitted by floating typeconnection 50 thus causing limiters 60 to move relative to cap 40.Preferably, pressure limiters 60 include bolt 61 secured to flange 43aby jam nuts 62, FIG. 7. In this manner, bolt 61, including extendedportion 61a, may be extended from reinforcing member 43 to apredetermined length for engagement with a portion of base 20 such aspads 28 provided at locations A, B, C and D. Pads 28 are secured, suchas by welding, to base 20 by members 29 which may comprise angles weldedto upper and lower flanges 23 and 24 respectively. Since pressurelimiters 60 and cap 40 are secured to reinforcing members 43 and haverelative movement therewith, the contact of extended portions 61a withpads 28 will limit the pressure exerted on seal member 21 by edge 44 ofcap 40 and the limiters may be adjusted to provide substantially equalpressure between the cap and the seal member along the continuoussealing contact of edge 44 and seal member 21. At least 3 limiters andpads are needed to establish a stable co-planar relationship between cap40 and base 20. The pads and limiters are preferably located at equallyradially spaced intervals with respect to cap 40.

Resilient members or stabilizers are preferably located at E, F, G andH, see FIG. 2, and comprise springs 76 preloaded in compression betweenframe 30 and cap 40 for stabilizing the relative multi-directionalmovement therebetween. Such preloading maintains plates 52 and 53 out ofcontact when cap 40 is not in closing engagement with base 20, see FIG.4. The amount of separation of plates 52 and 53 is limited by washers 56and hex nuts 57 as previously described. Stabilizers 70 are preferablylocated at the four locations E, F, G and H, however, more than fourstabilizers may be used if preferred. At least 3 stabilizers are neededto establish a stable co-planar relationship between frame 30 and cap 40and the stabilizers should be located at equally radially spacedintervals with respect to cap 40. A beneficial effect of stabilizers 70is that they stabilize cap 40 when in the open position to counteractfluttering of the floating cap which can be caused by high winds.

Preferably, stabilizers 70 include support plate 71 adjustably mountedby bolt 72 and slot 73 to member 31 of frame 30. Bolt 74 depends fromflange 71a and is fixedly attached thereto. Shaft portion 74a of bolt 74is secured for limited relative movement with reinforcing member 43 by aconventional locknut 75. Resilient stabilizing spring 76 surrounds shaftportion 74a of bolt 74 between flange 71a and reinforcing member 43.Precompression of spring 76 permits limited relative movement ofresilient member 43 with respect to frame 30 within the limits ofshoulder bolts 74 and locknut 75 as shown in phantom outline in FIG. 6.

Power for moving pivotable frame 30 is supplied by reversible electricmotor 80 located on support 80a near the base of stack 14, see FIG. 1.Screwjacks 81 and 82 are located on support 80a and are coupled to besimultaneously driven by motor 80. One of the screwjacks is a right-handscrew and the other is a lefthand screw. In this manner, when reversiblemotor 80 rotates in one direction the screwjacks will simultaneouslymove in opposite directions; that is, one screwjack will move upwardwhile the other moves downward. Screwjacks 81 and 82 are connected tocables 83 and 84 respectively. The cables are secured to circular tracklever arm 85 and the lever arm is secured to shaft 103. The cables 83and 84 are secured respectively to left and right positions (as viewedin FIG. 1) of circular track lever arm 85 using a suitable type ofsecuring device such as a clevis and pin 86. Therefore, when screwjacks81 and 82 are driven by motor 80, the connected cables 83 and 84 aresimultaneously moved in opposite directions thus rotating circular tracklever arm 85 and shaft 103 in a clockwise direction (as viewed inFIG. 1) and pivoting the closure which is secured to shaft 103 foropening stack 14. Altemately, when motor 80 is reversed, lever arm 85 isrotated counterclockwise to pivot the closure 10 for closing stack 14.Since both screwjacks 81 and 82 operate simultaneously, but in oppositedirections, there is always positive control of the closure at all timesduring opening and during closing of stack 14. Since the closure iscounterweighted, only a small torque is required to pivot closure 10 foropening and closing stack 14.

The beneficial effect of the circular track lever arm 85 can be realizedfrom FIG. 1 wherein it can be seen that cables 83 and 84 follow circulartrack 85a thus providing a cable pull which is always 90 degrees to thelever arm; that is, the line of action, designated a, of cable 84 isalways disposed at 90 from a radius designated r, struck from the centerof lever 85 and intersecting line a at thepoint where cable 84 isconnected to lever 85 by clevis and pin 86. This cable pull conditionwill exist at all points along cables 83 and 84 which are in engagementwith track 850. Therefore, engagement of cables 83 and 84 with track 85ashould be maintained at the clevis and pin 86 when lever 85 is rotatedto either fully open or close cap 40. In this manner, varying torqueacting on shaft 103 will be minimized.

The foregoing has illustrated a novel reliable closure for exhauststacks including a frame pivotally connected to a base, which baseissecured to the exhaust end of an exhaust stack; a cap connected to theframe by a floating connection operable to permit relativemulti-directional movement between the frame and the cap thus permittingthe cap to accommodate variations in alignment between the cap and thebase and to thereby align with the base for closing engagementtherewith; resilient stabilizing members connected to the frame and thecap so as to aid in stabilizing the relative multi-directional movementtherebetween; an improved seal member to seal the closing engagement ofthe cap and the base; and pressure limiters for limiting excessivepressure on the seal member and for maintaining substantially equalpressure between the cap and the seal member. I

Having thus described the invention in its best embodiment and mode ofoperation, that which is desired to be claimed by Letters Patent is:

l. A stack closure for closing the exhaust end of an exhaust stack toprevent the exhaust of gases therefrom and for opening said exhaust endto permit the exhaust of gases therefrom therefrom, closure comprising:

a base attached to said exhaust end;

a closure cap engageable with said base for closing said exhaust end;

a moveable support frame connected to said closure cap for moving saidclosure cap into and out of engagement with said base;

a floating connection means between said closure cap and said moveablesupport frame for aligning said closure cap with said base for positiveclosing engagement therewith;

a drive means for moving said support frame;

said floating connection means between said closure cap and said supportframe including loosely mounted bolts connecting said closure cap tosaid support frame for permitting random movement therebetween therebypermitting said closure cap to be selfaligning with said base;

a plurality of resilient members preloaded in compression between saidsupport frame and said closure cap for stabilizing said random movementtherebetween;

a resilient seal member mounted to one of said base and said closure capfor sealing against the exhaust of gases therebetween;

said closure cap including reinforcing means comprising metal membersrigidly attached to said closure cap in substantially co-planarrelationship with said support frame; and

a means for limiting pressure exerted on said seal member when saidclosure cap is pivoted into sealing engagement with said base,

said pressure limiting means comprising bolts extending from saidreinforcing means to a predetermined length for engagement with aportion of said base,

whereby engagement of said bolts with said base limits the pressureexerted on said seal member by said closure cap and provides asubstantially equal pressure therebetween.

1. A stack closure for closing the exhaust end of an exhaust stack toprevent the exhaust of gases therefrom and for opening said exhaust endto permit the exhaust of gases therefrom therefrom, closure comprising:a base attached to said exhaust end; a closure cap engageable with saidbase for closing said exhaust end; a moveable support frame connected tosaid closure cap for moving said closure cap into and out of engagementwith said base; a floating connection means between said closure cap andsaid moveable support frame for aligning said closure cap with said basefor positive closing engagement therewith; a drive means for moving saidsupport frame; said floating connection means between said closure capand said support frame including loosely mounted bolts connecting saidclosure cap to said support frame for permitting random movementtherebetween thereby permitting said closure cap to be self-aligningwith said base; a plurality of resilient members preloaded incompression between said support frame and said closure cap forstabilizing said random movement therebetween; a resilient seal membermounted to one of said base and said closure cap for sealing against theexhaust of gases therebetween; said closure cap including reinforcingmeans comprising metal members rigidly attached to said closure cap insubstantially co-planar relationship with said support frame; and ameans for limiting pressure exerted on said seal member when saidclosure cap is pivoted into sealing engagement with said base, saidpressure limiting means comprising bolts extending from said reinforcingmeans to a predetermined length for engagement with a portion of saidbase, whereby engagement of said bolts with said base limits thepressure exerted on said seal member by said closure cap and provides asubstantially equal pressure therebetween.